Pericarpium Citri reticulata is the dried pericarp of the young or immature fruits of Citrus reticulate Blanco and its cultivars (Fam. Rutaceae). The fallen young fruit is collected in May and June, dried in the sun and known commonly as "Geqingpi". The immature friut is collected in July and August, cut longitudinally into four-valved but connected at the base, removed from the emergence completely and dried in the sun, and known commonly as "Sihuaqingpi".

20% qing pi decoction could significantly prlong the prothrombin time, thrombin time and some thromboplastin time, which indicated that qing pi had significant anti-coagulation effect. Its decoction and ethanol extract had anti-thrombosis effect in vitro.